Wireless communication system

ABSTRACT

A wireless communication device for performing bi-directional communication using a frequency hopping method, in which the communication time at any one frequency can be varied. The user uses the dial to adjust the length of time during which a single frequency is used. Accordingly, if the volume of data is large, as in image data, the communication time can be increased. If the volume of data is small, as in voice data, the communication time can be decreased. If privacy is desirable, the communication time is decreased, whereas increasing the communication time will increase the transfer rate. Such settings can be made manually by the user to suit the user&#39;s needs, or can be made automatically based on the type of data being transferred.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system forperforming bidirectional communication between communication devicesusing a spread spectrum communications technique and particularly usinga frequency hopping method.

2. Description of the Related Art

There has been proposed a wireless communication system using a spreadspectrum communication method. This type of wireless communicationsystem employs a frequency hopping method to increase effectiveness andprivacy. Frequency hopping is performed according to a predeterminedrule defined by a spread code series.

That is, a frequency switching sequence (hereinafter referred to as"hopping pattern") used during communication is predetermined. All thecommunication devices in the communication system always follow the samehopping pattern Thus, transmission and reception of signals can beperformed by making the spread code series (frequency hopping pattern)common for a group of the communication devices.

SUMMARY OF THE INVENTION

FIG. 1 shows a structure of a conceivable communication device forperforming bi-directional communication with a remote communicationdevice according to a frequency hopping spread spectrum communicationmethod.

First, the transmission operations of the communication device will bedescribed below.

A synchronization circuit 4 includes a timer for generatingsynchronization signals. The spread code series generator 5 sequentiallyoutputs the predetermined spread code series in synchronization with thesynchronization signals.

The spread code series outputted from the spread code series generator 5is supplied to a frequency synthesizer 6. The frequency synthesizer 6generates frequency-hopping signals whose frequency hops from one toanother based on the supplied spread code series. The frequency-hoppingsignals serve as carrier waves for transmitting data to and forreceiving data from the remote communication device.

Thus, the frequency-hopping signals are outputted from the frequencysynthesizer 6, While hopping according to the spread code series insynchronization with the synchronization signals. Transmission data tobe transmitted to the remote communication device is modulated into aprimary modulation signal, before being inputted via a transmission datainput terminal 20 to the communication device. The primary modulationsignal is then multiplied by an up converter 3 with thefrequency-hopping signals outputted from the frequency synthesizer 6.Thus, the output frequency of the transmission signals are convertedfrom the primary modulation frequency. Thus, the transmission signalsare created with their frequency being spread or hopped. After thefrequency of the transmission signals is thus converted by the upconverter 3, the transmission signals are amplified by an amplifier 8.Then, the transmission signals pass through a switching device 10 beforebeing transmitted from an antenna 11 toward the remote communicationdevice.

Next, the reception operations of the communication device will bedescribed below.

When signals, transmitted from the remote communication device, arereceived at the antenna 11, the reception signals are separated from thetransmission signals by the switching device 10. The reception signalsare amplified by an amplifier 9, and inputted into a down converter 7.The down converter 7 converts the frequency of the reception signalsbased on the frequency-hopping signals supplied from the frequencysynthesizer 6. That is, the down converter 7 multiplies the receptionsignals with the frequency-hopping signals. Thus, the frequency of thereception signal is converted into the primary modulation frequency. Thereception signals are then demodulated and converted to reception databy a demodulator 12. This reception data is then outputted both to areception data output terminal 21 and to the synchronization circuit 4.

In the reception time slot, the synchronization circuit 4 generatessynchronization signals based on the reception data demodulated by thedemodulator 12. That is, the synchronization circuit 4 generatessynchronization signals when the reception data includes a specific bitarray. More specifically, the synchronization circuit 4 counts apredetermined length of time with using the timer after receiving thespecific bit pattern, and then generates synchronization signals. Thus,the synchronization circuit 4 can output synchronization signals whichare in synchronization with synchronization signals generated in theremote communication device. The spread code series generator 5sequentially outputs the predetermined spread codes in synchronizationwith the synchronization signals.

In the same manner as in the transmission time slot. the spread codeseries, outputted from the spread code series generator 5, is suppliedto the frequency synthesizer 6. The frequency synthesizer 6 generatesfrequency-hopping signals whose frequency hops from one to another basedon the inputted spread code series. The down converter 7 multiplies thereception signals with the frequency-hopping signals, to therebyde-spread the reception signals and accordingly create the outputsignals. The de-spread signals are then demodulated by the demodulator12 into reception data. The reception data is outputted from thereception data output terminal 21 and supplied into a data computingcircuit (not shown).

In this way, the communication device operates as both a transmitter anda receiver while the switching device 10 performs switching operation,to thereby achieve bidirectional communication.

As described above, the frequency of the frequency-hopping signals hopsaccording to the spread code series, which are outputted from the spreadcode series generator 5 in synchronization with the synchronizationsignals outputted from the synchronization circuit 4. Thus, thefrequency of the frequency-hopping signals hops at a fixed time interval(which will be referred to as a holding time T' hereinafter).

It is noted, however, that it takes a certain period of time for thefrequency-hopping signal to stabilize after the frequency of the signalhops. This time period will be hereinafter referred to as occupied timet. Further, with the hopping method, the amount of holding time T'allocated for actual communication at each frequency is set lower than amaximum limit, which is predetermined for the frequency-hoppingcommunication method in order to maintain privacy and to allow the useof multiple channels. The holding time T' is therefore set sufficientlysmaller than the maximum limit.

It is now assumed that the frequency of the frequency-hopping signalshops as shown in FIG. 2. For example, the frequency f hops from afrequency band f1 to a different frequency band f2. Directly after thefrequency hops from one frequency band to a next frequency band thefrequency is unstable during the occupied time t. Communication is notpossible during the occupied time t. The entire system must wait untilthe frequency has stabilized. As a result, the transmission speedbecomes lower in principle than that of a fixed carrier wave frequencycommunication used in normal amateur radios and the like. However, Interms of privacy, it is desirable to frequently hop the frequency todifferent frequencies rather than communicating entirely at a fixedcarrier wave frequency.

In view of the foregoing, It is an object of the present invention toprovide a wireless communication system capable of either increasingtransfer rate or improving privacy.

In order to attain the above and other objects, the present inventionprovides a wireless communication device for performing bi-directionalcommunication with a remote communication device using a frequencyhopping method, the device comprising: means for changing a frequency,at which communication is performed: means for performing communicationwith the changed frequency during a holding time; and means forcontrolling a length of the holding time and for controlling thecommunication means to perform communications according to thecontrolled holding time.

According to another aspect, the present invention provides a wirelesscommunication device for performing bi-directional communication with aremote communication device using a frequency hopping method, the devicecomprising: means for performing communication with a remotecommunication device at a frequency; means for detecting an error rateof signals received from the remote communication device at thefrequency; memory means for storing a predetermined error rate referencevalue; means for determining whether or not the detected error rate ofthe communicated signals is higher than the predetermined error ratereference-value; and means for changing the frequency into anotherfrequency when the error rate determining means deter-mines that thedetected error rate is higher than the predetermined error ratereference value, the frequency changing means controlling thecommunication means to perform communications according to the changedfrequency.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of a communication device used in aconceivable wireless communication systems;

FIG. 2 is a graph showing the relationship between carrier wavefrequencies and time in the conceivable wireless communication systems.

FIG. 3 is a block diagram of a communication device for achievingwireless communication according to a first embodiment of the presentinvention:

FIGS. 4(a) and 4(b) are flowcharts showing the processes of twocommunication devices 1a and 1b of the first embodiment that are engagedin communication with each another;

FIG. 5 is a diagram showing the timing for wireless communicationperformed in the first embodiment;

FIG. 6 is an explanatory diagram of the transmission data format used inthe first embodiment;

FIGS. 7(a) and 7(b) are flowcharts showing the processes of twocommunication devices of a modification of the first embodiment that areengaged in communication with each another;

FIG. 8 is a diagram showing the timing for wireless communicationperformed in the modification of the first embodiment;

FIGS. 9(a) and 9(b) are flowcharts showing the processes of twocommunication devices of a second embodiment that are engaged incommunication with each another;

FIG. 10 is a diagram showing the timing for wireless communicationperformed in the second embodiment;

FIG. 11 is an explanatory diagram of a transmission data format used inthe second embodiment;

FIG. 12 is a diagram showing the timing for wireless communicationperformed in a modification of the second embodiment;

FIGS. 13(a) through 13(c) are explanatory diagrams showing therelationship between the holding time and the packet length;

FIG. 14 is a block diagram showing the construction of a communicationdevice of a third embodiment;

FIG. 15 is a diagram showing the timing for frequency changes performedin the communication device of the third embodiment;

FIG. 16 is a block diagram showing the construction of a communicationdevice of a first modification of the third embodiment;

FIG. 17 is a block diagram showing the construction of a communicationdevice of a second modification of the third embodiment;

FIGS. 18(a) and 18(b) are flowcharts showing the operations performed ina pair of communication devices each of which has the structure of FIG.16;

FIG. 18(c) is a flowchart showing relationship between timings of therespective steps in FIGS. 18(a) and 18(b);

FIG. 19 is a flowchart showing the operations performed in thecommunication device of FIG. 1 in response to transmission from thecommunication device as shown in FIG. 18(a); and

FIG. 20 is a diagram showing the format of data transmitted by thecommunication device of FIGS. 14, 16, and 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A wireless communication system according to preferred embodiments ofthe present invention will be described while referring to theaccompanying drawings.

A first embodiment will be described below with reference to FIGS. 3through 6.

As shown in FIG. 3, a communication device 1 of the present embodimentis provided with; a transmission data input terminal 20, a receptiondata output terminal 21, a synchronization unit 25, a spread code seriesgenerator 26, an antenna 33, a demodulator 34, a hopping table 35, adata adding device 36, a primary modulator 37, a control unit 38, acommunication unit 50, a transmission data primary modulator 60, and adata controller 62.

The control unit 38 is for controlling the entire device 1, and forcontrolling the holding time T according to the present embodiment. Thecontrol unit 38 is constructed from a CPU (not shown) for performing anentire control. The control unit 38 is provided with: a dial unit 39, amemory cry unit 40, and a timer unit 41. The dial unit 39 includes adial knob for setting the holding time T. A user can rotate the dialknob to thereby set the holding time T to his/her desired length. Thememory unit 40 is constructed from a RAM and a ROM, for example. Thememory unit 40 previously stores therein data of the occupied time twhich is predetermined as the length of time period during which thefrequency of a frequency-hopping signal is unstable after the frequencyis hopped. The holding time T, set by the user's manipulation of thedial unit 39, is also stored in the memory unit 40. The timer unit 41 isfor counting the occupied time t after the frequency of thefrequency-hopping signal is hopped. The timer unit 41 is also forcounting a time length (T-t) obtained by subtracting the occupied time tfrom the holding time T after the occupied time t has elapsed after thefrequency hopping is attained.

The control unit 38 is also for outputting data of the user's setholding time T to the primary modulator 37. The primary modulator 37 isfor modulating the holding time data into a holding time data signal ofthe primary frequency f_(IF).

The control unit 38 operates in response to synchronization signalssupplied from the synchronization unit 25 which will be described later.The control unit 38 produces a predetermined bit pattern correspondingto the synchronization signal, and outputs the bit pattern also to theprimary modulator 37.

The data controller 62 is connected to a data input/output unit (notshown) such as a telephone circuit, an ISDN circuit, a telephonereceiver, a facsimile data reading unit, and the like. For example, whenthe communication device 1 is mounted to a telephone, the datacontroller 62 is connected to a telephone circuit or an ISDN circuit anda telephone receiver. When the communication device 1 is mounted to afacsimile machine, the data controller 62 is connected to a telephonecircuit or an ISDN circuit and a facsimile data reading unit. When thecommunication device 1 is mounted to a device which can serve as both afacsimile machine and a telephone, the data controller 62 is connectedto a telephone circuit or an ISDN circuit, a telephone receiver, and afacsimile data reading unit.

The data controller 62 is for receiving, from the data input/output unit(such as the telephone circuit), transmission data, such as telephonedata or facsimile data, to be transmitted to a remote communicationdevice. The data controller 62 is also for receiving data of theoccupied time t and data of the user's set holding time T from thecontrol unit 38. The data controller 62 creates transmission data forthe time length (T-t) based on the received data. The data controller 62is also for receiving reception data, which has been transmitted fromthe remote communication device and inputted from the reception dataoutput terminal 21. The data controller 62 transfers the reception datato the data input/output unit such as the telephone circuit.

The data primary modulator 60 is for modulating the transmission data,outputted from the data controller 62, into a transmission data signalof the primary frequency f_(IF).

The data adding device 36 is for adding the holding time data signal, asa header, to the transmission data signal, thereby creating atransmission signal in a data format shown in FIG. 6. The data addingdevice 36 outputs the transmission signal to the communication unit 50.It is noted that although not shown in the FIG. 6, the data addingdevice 36 also adds, to the transmission signal, the predetermined bitpattern, indicative of the synchronization signal, which is suppliedfrom the control unit 38 via the primary modulator 37.

The communication unit 50 includes: a frequency synthesizer 28, an upconverter 22, a down converter 29, amplifiers 30 and 31, and a switchingdevice 32. The frequency synthesizer 28 is for receiving spread codessequentially supplied from the spread code series generator 26 and forgenerating frequency-hopping signals whose oscillating frequencies farhop according to the supplied spread codes. The frequency-hoppingsignals are supplied to both the up converter 22 and the down converter29. The up converter 22 is for receiving both the frequency-hoppingsignals with frequencies f_(N') and the transmission signals with thefrequency f_(IF). The up converter 22 mixes or multiplies thefrequency-hopping signals with the transmission signals f_(IF). Theresultant transmission signals with their frequency f_(N) (=f_(N'+f)_(IF)) are supplied to the amplifier 30. The transmission signals arethen amplified by the amplifier 30. The switching device 32 is forselectively guiding the transmission signals to the antenna 33 andguiding reception signals picked up at the antenna 33 to the amplifier31. When the transmission signals are guided to the antenna 33 via theswitching device 32, the transmission signals of the frequency f_(N) aretransmitted from the antenna 33 to the remote communication device.

Signals of the frequency f_(N) are also transmitted from the remotecommunication device and picked up by the antenna 33. The switchingdevice 32 guides the reception signals to the amplifier 31. Theamplifier 31 is for amplifying the reception signals. The down converter29 is for receiving both the reception signals of the frequency f_(N)and the frequency-hopping signals of the frequency f_(N'). The downconverter 29 mixes or multiplies the reception signals and thefrequency-hopping signals, thereby creating reception data signals withfrequency f_(IF). The reception data signals are supplied to thedemodulator 34. The demodulator 34 is for demodulating the receptiondata signals into reception data, and for supplying the reception datainto both the control unit 38 and the reception data output terminal 21.

The synchronization unit 25 includes a timer (not shown), and is foroutputting synchronization signals at a fixed frequency to the controlunit 38 and to the spread code series generator 26. The synchronizationunit 25 is designed to attain synchronization with the remotecommunication device. That is, during a transmitting time slot, thesynchronization unit 25 outputs synchronization signals at the fixedfrequency. The synchronization signals are transmitted to the remotecommunication device in the form of the predetermined bit patterns.During a receiving time slot, on the other hand, the synchronizationunit 25 serves to receive the reception data from the demodulator 34 viathe control unit 38 and to detect whether or not the reception dataincludes the predetermined bit pattern indicative of a synchronizationsignal. When receiving the predetermined bit pattern, thesynchronization unit 25 counts the predetermined length of time withusing the timer, and then generates synchronization signals.

The hopping table 35 stores therein a series of spread codes as shown inthe Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Spread code series                                                                       Series no. 1      2    3    4    . . .                                        Spread code                                                                              S1     S2   S3   S4   . . .                             ______________________________________                                    

Thus, the table 35 contains data of a randomly-arranged plurality ofspread codes. The spread code series S1, S2, . . . correspond topredetermined hopping frequencies f_(N') (f_(N'1), f_(N'2), . . . ) ofthe frequency-hopping signals to be outputted from the frequencysynthesizer 28.

The spread code series generator 26 is for receiving the synchronizationsignals from the synchronization unit 25 and for receiving instructionsignals outputted from the control unit 38. When the instruction signalsare to hop the frequency of the frequency-hopping signals to the nextfrequency, the spread code series generator 26 selects, from the hoppingtable 35, a spread code that appears next to a spread code correspondingto the current frequency of the frequency-hopping signals, and outputsthe selected spread code to the frequency synthesizer 28. The frequencysynthesizer 28 outputs frequency-hopping signals whose frequency fcorresponds to the received spread code S.

Next, bi-directional communication attained between two communicationdevices 1a and 1b will be described with reference to flowcharts ofFIGS. 4(a) and 4(b) and the timing chart of FIG. 5.

It is noted that each of the communication devices 1a and 1b has thesame structure as shown in FIG. 3. It is assumed that the communicationdevice 1a has all the components shown in FIG. 3 which will be referredto as the reference numbers appearing in the figure followed with thesymbol "a". Similarly, it is also assumed that the communication device1b has all the components shown in FIG. 3 which will be referred to asthe reference numbers appearing in the figure followed with the symbol"b". It is noted that the hopping tables 35a and 35b in thecommunication devices 1a and 1b store therein the same spread codeseries as shown in Table 1.

It is further noted that steps in FIGS. 4(a) and 4(b), whose final twodigits match with each other, are performed at about the same time. Itis noted that in each communication step performed between the devices1a and 1b, synchronization is attained between the devices 1a and 1bwith using transmission of a synchronization signal in the form of thepredetermined bit pattern. However, for simplicity and clarity, thedescription for the processes for attaining the synchronization isomitted from the following description. As shown in FIG. 6, the formatof each transmission data signal includes holding time data in theheader, followed by transmission data.

Before the communication is performed, a user of the communicationdevice 1a sets his/her desired holding time Ta through manipulating thedial unit 39a. The holding time data is stored in the memory unit 40a.Similarly, another user of the communication device 1b sets his/herdesired holding time Tb through manipulating the dial unit 39b. Theholding time data is stored in the memory unit 40b.

First, the process for the communication device 1a will be describedwith reference to FIG. 4(a).

At the beginning of the process, the control unit 38a outputs afrequency hop instruction signal to the spread code series generator26a. In 5101, the spread code series generator 26a selects a spread codethat appears in the hopping pattern table 35a next to a spread codecorresponding to the current frequency. The spread code series generator26a outputs the selected spread code to the frequency synthesizer 28a.It is noted that the generator 26a outputs the first spread code S1 inS101 of the first routine. As a result, the frequency synthesizer 28produces a frequency-hopping signal whose frequency corresponds to thesupplied spread code.

The control unit 38a then waits in S102 until the prescribed occupiedtime t elapses after the frequency has hopped to the current frequency.To accomplish this, the control unit 33a reads data of the prescribedoccupied time t from the memory unit 40a, sets the timer unit 41a tothis occupied time t, and starts the timer 41a to count down the time t.The control unit 38a determines that the time has elapsed when the timerunit 41a reaches zero. The control unit 38a continues monitoring thetimer unit 41a in S102 until the occupied time t has elapsed ("yes" inS102), at which time the current frequency of the frequency-hoppingsignal becomes stable.

Next, data of the holding time Ta is read from the memory unit 40a, andthe timer unit 41a is set to the time Ta in S103. The timer unit 41abegins counting down a time length (Ta-t) which is obtained bysubtracting the occupied time t from the holding time Ta.

The data controller 62a creates transmission data based on the holdingtime Ta and transmits that data to the communication device 1b in S104.More specifically, the data controller 62a receives data from the datainput/output unit such as the telephone circuit, and createstransmission data for the time length (Ta-t). The transmission data isthen modulated at the primary modulator 60a, and inputted into thetransmission data input terminal 20a. At the same time, the holding timedata is outputted from the control unit 38a to the primary modulator 37awhere the holding time data is modulated. The modulated holding timedata is added to the header of the transmission data at the data addingdevice 36a as shown in FIG. 6. The transmission data with the holdingtime indicating header is sent through the up. converter 22a, theamplifier 30a, and the switching device 32a, before being transmittedthrough the antenna 33a to the communication device 1b. The transmissionis determined to be complete when the timer unit 41a reaches zero.

After transmission has completed, the control unit 38a outputs afrequency hop instruction signal to the spread code series generator 26ain S107. As a result, the frequency of the frequency-hopping signal ishopped to a frequency which corresponds to a spread code that appears inthe table 35 next to the latest-used spread code. The control unit 38athen determines whether the prescribed occupied time t has elapsed inS108, checking repeatedly until the time t has elapsed ("yes" in S108).When the occupied time t elapses, the newly-hopped frequency becomesstable, and the communication device 1a begins receiving reception datafrom the communication device 1b in steps S110-S112.

That is, reception signals transmitted from the communication device 1bare received at the antenna 33a of the communication device 1a. Thereception signals pass through the switching device 32a, the amplifier31a, the down converter 29a, and the demodulator 34a, before beinginputted into the control unit 38a. The control unit 38a reads theholding time data from the header of the reception data in S110. Theholding time data indicates a holding time Tb which has been set by thedial unit 39b in the communication device 1b. In S111, the timer unit41a is set to the holding time Tb. The timer unit 41a begins countingdown a time length (Tb-t) which is obtained by subtracting the occupiedtime t from the holding time Tb. The remaining data is then received inS112. The received data is inputted to the data controller 62 throughthe terminal 21. The reception data is supplied to the data input/outputunit such as the telephone circuit. When the timer unit 41a reacheszero, all the data is determined to have been received. The process isrepeated from step S101.

Next, the process for the communication device 1b will be described. Thedescription will be brief since the process for the communication device1b is almost the same as that for the communication device 1a exceptthat the order of transmission and reception is reversed.

At the beginning of the process, and at the same time as the executionof S101 by the communication device 1a, the control unit 38b outputs afrequency hop instruction signal to the spread code series generator26b, causing the communication device 1b to hop in S201 to the samefrequency as the communication device 1a. Simultaneously with S102 ofthe process for the communication device 1a, the control unit 38bdetermines whether the occupied time t has elapsed in S202, checkingrepeatedly until the time t has elapsed ("yes" in S202). Reception datais then received from the communication device 1b in S204-S206.

That is, in S204, the control unit 38b reads the holding time dataattached to the received data. In S205, the timer unit 41b is set to theholding time Ta, indicated by the holding time data, which time has beenset by the dial unit 39a in the communication device 1a. The timer unit41b begins counting down the time length (Ta-t). The remaining data isthen received in S206.

After reception has completed, the control unit 38b outputs a frequencyhop instruction signal to the spread code series generator 26b, causingthe communication device 1b to hop in S207 to the same frequency as thecommunication device 1a in 6107. After the occupied time t has elapsed("yes" in S208), the communication device 1b transmits transmission datato the communication device 1a in S209-S210.

That is, in S209, the control unit 38b sets the timer unit 41b to theholding time Tb which has been set by the dial unit 39b. The timer unit41b begins counting down the time length (Tb-t). Transmission data iscreated based on the holding time Tb, and the transmission data and theholding time data is transmitted to the communication device 1a in S210in the same manner as in S104. After the transmission has completed, thecompletion of the transmission is determined when the timer unit 41breaches zero. Then, the process is repeated from S201.

FIG. 5 shows a timing chart of the bi-directional communication attainedbetween the communication devices 1a and 1b. As can be seen from thediagram, when the devices hop to a frequency f1, the communicationdevice 1a transmits data to the communication device 1b during theholding time Ta which is set at the communication device 1a. Then, thefrequency hops from the frequency f1 to another frequency f2. At thefrequency f2, the communication device 1b transmits data to thecommunication device 1b during the holding time Tb which is set at thecommunication device 1b. Then, the frequency hops from the frequency f2to another frequency f3. At the frequency f3, the communication device1a again sends data to the communication device 1b during the holdingtime Ta. It is noted that the frequency hops to the frequencies f1, f2,f3, . . . when the spread code generator 26 outputs the spread codes S1,S2, S3, . . . selected from the hopping pattern table 35.

It is apparent from the above description that the holding time lengthis determined by a communication device which is in a transmitting timeslot. In addition, each of the holding time lengths Ta and Tb includesthe occupied time t therein. The length of time possible for performingdata communication is equal to a time length obtained by subtracting theoccupied time t from the holding time Ta or Tb. According to the presentembodiment, the control unit 38 serves to control the holding time Tthrough the processes of S103 and S104, S110 and S111, S204 and S205,and S209 and S2l0. The user can freely manipulate the dial unit 39 inthe control unit 38. The user can increase the length of the holdingtime T, thereby decreasing the ratio of the occupied time t with respectto the holding time T and increasing the transfer rate. The user canalso decrease the length of the holding time T, thereby increasing thetotal number the frequency hops in a single communication. This willincrease privacy or secrecy of the communication contents.

Various modifications for the present embodiment will be describedbelow.

A first modification is shown in FIGS. 7(a) and 7(b) and FIG. 8. In thismodification, the processes of S107 and S108 shown in FIG. 4(a) for thecommunication device 1a are replaced with processes of S107' forswitching from transmission to reception. The processes of S207 and S208shown in FIG. 4(b) for the communication device 1b are replaced withprocesses of S207' for switching from reception to transmission. Morespecifically, as shown in FIG. 7(a), the communication device 1a hops toa first frequency f1 in S101; transmits data at that frequency f1 inS102-S104; and then receives data at the same frequency f1 in S110-S112.Then, the same operations are performed repeatedly through S101 throughS112 while repeatedly hopping-the frequency. As shown in FIG. 7(b), thecommunication device 1b receives data at the same frequency f1 inS202-S206; and then transmits data also at the same frequency f1 in5209-S210. In short, according to this modification, as shown in FIG. 8,hopping is performed once for every cycle of transmission and reception.That is, bi-directional communication is performed during the total timeTa and Tb at each frequency. This modification has the same effect asthat obtained in the above-described embodiment.

A second modification for the present embodiment will be describedbelow.

According to the present modification, the holding time T is setautomatically by the communication device 1 according to a type of datato be transmitted. That is, according to this modification, in S103 ofthe process for the communication device 1a, the timer unit 41a isautomatically set to a holding time T_(VO) when the data to betransmitted is voice data (telephonic data), and is set to a holdingtime T_(FA) when the data to be transmitted is facsimile data. It isnoted that T_(FA) is set to be longer than T_(VO) and not to exceed themaximum limit predetermined for the wireless communication method.

In this modification, when the data controller 62 receives transmissiondata from the data input/output unit such as the telephone circuit, thedata controller 62 detects whether or not the received data contains CNGsignals, for example. The data controller 62 supplies detection dataindicative of the detected result to the control unit 38. When thedetection data indicates that the transmission data contains CNGsignals, because the data is considered facsimile data, the control unit38 sets the timer unit 41a to T_(FA) in S103. When the detection dataindicates that the transmission data does not contain CNG signals,because the data is considered voice data, the control unit 38 sets thetimer unit 41a to T_(VO) in S103.

Especially when the communication device 1 is used both for a telephoneand a facsimile machine, the control unit 38 ordinarily sets the timerunit 41a to T_(VO) in S103. The control unit 38 sets the timer unit 41ato T_(VA) only when a facsimile start button is pushed for transmittingfacsimile data.

Thus, the holding time T_(FA) for transmission of facsimile data is setlonger than the holding time T_(VO) for transmission of voice data. Thisis because facsimile data includes a comparatively large amount of data,and usually requires an increased transfer rate more than increasedprivacy, whereas voice data includes a comparatively small amount ofdata and usually requires increased privacy more than an increasedtransfer rate. Thus, by changing the holding time length to a valueappropriate for the type of data being transmitted and received,required property, i.e. either the transfer rate or the privacy, can beimproved.

Alternatively, the holding time T may be set automatically by thecommunication device 1 according to a type of the communicationdevice 1. More specifically, in S103 of the process for thecommunication device 1a, the control unit 38a may automatically set thetimer unit 41a to a holding time T_(FA) when the device 1a is afacsimile or to the other holding time T_(VO) when the device 1a is atelephone. Then, in S104, the control unit 38a produces an ID signalindicative of the type of the communication device 1a, and adds the IDsignal to the transmission data in place of the holding time data. Inthis case, the communication device 1b determines the type of thecommunication device 1a in S204 based on the received ID signal. InS205, therefore, the control unit 38b sets the timer unit 41b to eitherT_(FA) or T_(VO) based on the determined result.

Thus, by changing the holding time length to a value appropriate for thetype of data being transmitted and received, required property, i.e.,either the transfer rate or privacy, can be improved.

Alternatively, the memory unit 40 may previously store therein a holdingtime changing table containing data of a randomly-arranged plurality ofholding time lengths T. The control unit 38a may read in S103 a holdingtime value in order from the table every time a new bidirectionalcommunication process is begun. The control unit 38a uses the selectedholding time for the current communication session. In this way, thecurrently-used holding time will always be different from thepreviously-used holding time.

Alternatively, the holding time length T may be changed in S103 usingthe hopping pattern table 35 as shown in the Table 2 below.

                  TABLE 2                                                         ______________________________________                                        Series No. 1         2     3       4   . . .                                  Spread code                                                                              S1        S2    S3      S4  . . .                                  Holding time                                                                             T1        T2    T3      T4  . . .                                  ______________________________________                                    

This hopping table 35 is prepared through combining the hopping table 35shown in the Table 1 with the above-described holding time changingtable. In this case, every time the frequency hops, the holding time forthe frequency also changes. With this method, it will be extremelydifficult for a third party to intercept communication data because notonly does the frequency change but also the holding time changes. Hence,privacy or secrecy can be further improved.

Next, a wireless communication system according to a second embodimentof the present invention will be described while referring to FIGS. 9(a)and 9(b) and 10 wherein like parts and components are designated by thesame reference numerals to avoid duplicating description.

The structure of the wireless communication device 1 of the secondembodiment is the same as that of the wireless communication device ofthe first embodiment shown in FIG. 3. Therefore, a description of thatstructure will be omitted.

According to the present embodiment, the memory unit 40 previouslystores, in its prescribed area, data of a basic holding time T_(H) of afixed length. The memory unit 40 further stores therein a holding timechanging pattern as shown in Table 3 below in its another prescribedarea.

                                      TABLE 3                                     __________________________________________________________________________    Number     Pattern of change (hop data)                                                     ##STR1##                                                        __________________________________________________________________________

More specifically, in one communication device 1a, the memory unit 40apreviously stores therein data of the basic holding time T_(H) of thefixed length and the holding time changing pattern. Similarly, also inthe communication device 1b, the memory unit 40b stores therein theholding time T_(H) and the holding time changing pattern. It is notedthat the holding time changing pattern stored in-the communicationdevice 1b may be the same as or different from that stored in thecommunication device 1a.

It is further noted that according to the present embodiment, thetransmission data signal is created by the data adding device 36 in aformat as shown in FIG. 11. That is, a hop data flag is added to an endof the transmission data in accordance with the holding time changingpattern as will be described below.

Next, bi-directional communication between the two communication devices1a and 1b will be described with reference to the flowcharts in FIGS.9(a) and 9(b) and the timing-chart of FIG. 10.

It is noted that steps in FIGS. 9(a) and 9(b), whose final two digitsmatch with each other, are performed at about the same time. It isfurther noted that in each communication step, synchronization isattained between the communication devices 1a and 1b throughtransmission of a synchronization signal in the form of thepredetermined bit pattern. The description for the synchronizationattaining operation is, however, omitted from the following descriptionfor the simplicity and clarity.

First, the process of the communication device 1a will be describedbelow with reference to FIG. 9(a).

At the beginning of the process, the control unit 38a outputs afrequency hop instruction signal to the spread code series generator 26ain S301. The spread code series generator 26a selects a spread codeappearing in the hopping table 35 next to the latest-selected spreadcode. It is noted that the spread code SI is selected in S301 during thefirst routine. The generator 26a outputs the selected spread code to thefrequency synthesizer 28, which in turn produces a frequency-hoppingsignal whose frequency corresponds to the selected spread code. In thiscase, the frequency synthesizer 28 outputs a frequency-hopping signalwith frequency f1.

The control unit 38a then waits until the occupied time t has elapsed inS302. When the occupied time t has elapsed ("yes" in S302), the currentfrequency becomes stable. Then, the control unit 38a sets a hop dataflag in S303 according to the holding time changing pattern of Table 3stored in the memory unit 40a. That is, the hop data flag is set basedon current hop data in the holding time changing pattern. For example,in S303 of the first routine, the hop data flag is set based on hop dataappearing at the number "1" in the Table 3. In S303 of the secondroutine, the hop data flag is set based on hop data appearing at thenumber "2". Thus, in S303 of the n-th routine where 1≦n≦k, the hop dataflag is set based on hop data appearing at the number "n". It is notedthat the hop data flag is set to "on" if the current hop data in thetable is "change" or set to "off" if the current hop data in the tableis "stay." In this example, because "stay" is stored at the number "1",the hop data flag is set to "off". Also in S303, the timer unit 41a isset to the basic holding time T_(H), data of which is stored in thememory unit 40a.

It is noted that after the hop data corresponding to number "1" is thusused in S303 of the first routine, then the hop data corresponding tonumber "2" is set to the hop data flag in S303 of the next routine.After the hop data for number "k" is used, the hop data starts over atnumber "1". The data controller 62a creates transmission data based onthe basic holding time T_(H), and transmits the transmission data to thecommunication device 1b in S304. More specifically, the data controller62a creates transmission data for the time length of the basic holdingtime T_(H). The transmission data is modulated by the primary modulator60a, and inputted into the transmission data input terminal 20a. At thesame time, the control unit 38a outputs the hop data flag to the primarymodulator 37a where it is modulated. The modulated hop data flag is thenadded to the end of the transmission data by the data adding device 36a.The transmission data with the hop data flag shown in FIG. 11 is sentthrough the up converter 22a, the amplifier 30a, and the switchingdevice 32a, before being transmitted from the antenna 33a to thecommunication device 1b. The transmission is determined to be completewhen the timer unit 41a reaches zero.

After transmission has completed, in S305 the control unit 38a reads thehop data flag that has been set in S303. If the hop data flag is "on," aspread code appearing in the spread code series next to thelatest-selected spread code is selected, and the frequency of thefrequency-hopping signal is hopped to the corresponding frequency inS306. The control unit 38a then determines whether the occupied time thas elapsed in S307, checking repeatedly until the time t has elapsed("yes" in S307). When the occupied time t elapses, the newly-setfrequency becomes stable, and the communication device 1a beginsreceiving data from the communication device 1b in S309. When, in S305the hop data flag is "off," on the other hand, the process skips fromS305 to S309 without updating the spread code and without hopping to thenext frequency. The communication device 1a therefore begins receivingdata from the communication device 1b in S309 at the unchangedfrequency.

Signals received by the antenna 33a pass through the switching device32a, the amplifier 31a, the down converter 29a, and the demodulator 34aand are inputted into the control unit 38a. The control unit 38a readsthe hop data flag from the received data and determines in S310 whetherthe flag is "on" or "off." If the hop data flag is "on," the processreturns to S301, in which step the next spread code in the spread codeseries is generated, and the frequency is hopped to the next frequency.The process then continues as described above from S302. However, if thehop data flag in S310 is "off," the process proceeds to S303 withoutupdating the spread code and without hopping to a new frequency.

Next, the process for the communication device 1b will be describedbelow with reference to FIG. 9(b). The description will be brief sincethe process is almost the same as that for the communication device 1aexcept that the order of transmission and reception is reversed.

At the beginning of the process, and at the same time as the executionof S301 in the process for the communication device 1a, the control unit38b outputs a frequency hop instruction signal to the spread code seriesgenerator 26b, causing the communication device 1b to hop in S401 to thesame frequency hopped to by the communication device 1a. Simultaneouslywith S302 of the process for the communication device 1a, the controlunit 38b determines whether the occupied time t has elapsed in S402,checking repeatedly until the time t has elapsed ("yes" in S402). Datais then received from the communication device 1a in S404.

The control unit 38b reads the hop data flag from the received data, anddetermines in S405 whether the flag is "on" or "off." If the hop dataflag is "on," the next spread code in the spread code series isgenerated, and the frequency is hopped to the corresponding frequency inS406. When the control unit 38b determines that the occupied time t haselapsed ("yes" in S407), the process proceeds to S408. When, in S405 thehop data flag is "off," on the other hand, the process skips from S405to S408 without updating the spread code and without hopping to a newfrequency.

In S408, the control unit 38b creates the hop data flag according to theholding time changing pattern (Table 3, for example) stored in thememory unit 40b of the communication device 1b. That is, the hop dataflag is set to "on" when the current hop data in the table is "change"or set to "off" when the current hop data in the table is "stay" in thesame manner as in the communication device 1a in S303.

The data controller 62b creates transmission data based on the temporaryholding time T_(H) and transmits the data in S409. After transmissionhas completed, in S410 the control unit 38b reads the hop data flag thathas been set in S408. If the hop data flag is "on," the process returnsto S401 in which step the next spread code in the spread code series isgenerated, and the frequency is hopped to the corresponding frequency.The process continues as described above from S402. However, if the hopdata flag is "off," the process proceeds to S404 without updating thespread code and without hopping to a new frequency.

FIG. 10 shows the timing chart of operations during the above-describedbidirectional communication attained between the communication devices1a and 1b. As can be seen from the diagram, the devices 1a and 1bsimultaneously hop to the frequency f1 in S301 and S401. Because the hopdata for the number "1" in the holding time changing pattern (Table 3)of the communication device 1a is "stay," the communication device 1asets the hop data flag to "off" in S303 of the first routine.Accordingly, after the communication device 1a transmits data to thecommunication device 1b at the frequency f1 for the holding time T_(H),the frequency f1 is maintained unchanged.

In this example of FIG. 10, it is assumed that the hop data for thenumber "1" in the holding time changing pattern stored in thecommunication device 1b is "change." In this case, the communicationdevice 1b sets the data flag to "on" in S408 of the first routine. Thus,after the communication device 1b transmits data to the communicationdevice 1a at the frequency f1 for the basic holding time T_(H) in S409,the frequency is hopped to the frequency f2 in S401.

Thus, the hop data flag is set to "on" or "off" according to the holdingtime changing pattern, and the decision to hop to the next frequency ornot is determined by the hop data flag. Accordingly, the hop data flagdetermines an actual holding time during which each frequency is held.In this example of FIG. 10, the frequency f1 is held for the actualholding time of 2T_(H) +t, and the frequency f2 is held for the actualholding time of T_(H) +t.

As described above, in the wireless communication system of the presentembodiment, it will become extremely difficult for a third party tointercept communication signals, because not only is the frequency beingchanged, but also the actual holding time length is being changed.Hence, privacy is enhanced.

A modification of the second embodiment will be described below.

The wireless communication system of the modification is designed toperform transmission using a packet exchange system. That is, eachcommunication device 1 is provided with a buffer memory for temporarilystoring transmission data. The data controller 62 is designed to dividethe stored transmission data into equal blocks or packets, beforetransmitting these packets to a remote communication device 1.

The communication device 1 of the present modification stores thereindata of the basic holding time T_(H) in the memory unit 40a as eachpacket length L_(PAC). The communication device 1 also creates andstores a changing pattern shown in Table 4 below in the memory unit 40.

                  TABLE 4                                                         ______________________________________                                        Chang-  ing  pattern                                                                 ##STR2##                                                               ______________________________________                                    

The changing pattern is for setting the possible transmission time(i.e., a time length obtained by subtracting the occupied time t fromthe actual holding time) to be an integral multiple of the basic holdingtime T_(H). In other words, the possible communication time is set ton×T_(H), where n is an integer. The changing pattern is also for settingthe actual holding time (t+n×T_(H)) not to exceed the predeterminedmaximum time limit for the frequency hopping wireless communications.

According to the present modification, when the user at thecommunication device 1a desires to transmit data to the communicationdevice 1b through the packet exchange system, the communication device1a is controlled as described below.

That is, in FIG. 9(a) of the second embodiment, the communication device1a is designed to perform the reception process in S309 and S310 whenthe hop data flag is set to "off" In S305. Contrarily, according to thepresent modification, when the hop data flag is "off" in S305, theprogram proceeds to 2 in FIG. 9(a), and continues transmissionprocessing from S303. Similarly, the communication device 1b iscontrolled so that when the hop data flag is "off" in S405, the programproceeds to 4 in FIG. 9(b), and continues reception processing fromS404. The remaining steps are the same as those of the secondembodiment.

FIG. 12 shows a timing chart indicative of the operations performed inthe present modification. It is apparent that the possible communicationtime (i.e., the time length obtained by subtracting the occupied time tfrom the actual holding time) is set n times the packet length L_(PAC)(=T_(H)) (four times, in this case).

It is noted that if the possible communication time is different from ntimes the packet length L_(PAC), then remainder time will be produced asshown in FIG. 13(b), during which data cannot be transferred.Accordingly, the transfer rate cannot be improved sufficiently.Contrarily, because the possible communication time is set n times thepacket length L_(PAC) in the present modification, then no remaindertime will be produced, as shown in FIG. 13(a), and the transfer rate canbe sufficiently increased.

It is additionally noted that when the total number of packets that aredesired to be sent is m, it is desirable to set the value of n so thatm=n×p, where p is an integer. If this relation between m and n is notsatisfied, no data will be transferred during a gap of at least onepacket length L_(PAC) after the last packet has been sent, as shown inFIG. 13(c). As a result, the transfer rate cannot be sufficientlyincreased. However, if the relationship between m and n described aboveis met, a gap in transmission will not occur, and the transfer rate canbe sufficiently increased.

A third embodiment will be described below with reference to FIGS. 14,15, and 20.

According to the third embodiment, the current frequency is hopped tothe next frequency when the communication under the current frequency isdetected to have a high error rate.

More specifically, according to the communication device 1 of thepresent embodiment, when receiving reception data from a remotecommunication device, the error rate of the received signals is firstdetected. The detected error rate is then compared with a predeterminedfirst error rate reference value which is stored in the communicationdevice 1. When the detected error rate becomes higher than the referencevalue, the current frequency is changed to the next frequency accordingto the hopping pattern table 35.

According to the third embodiment, the data format of the transmissiondata signal (reception data signal) is designed as shown in FIG. 20. Thetransmission data signal is constructed from: transmission data(communication data), i.e., actual data desired to be sent to a remotecommunication device: error correction data to be used for correctingerrors in the transmission data; and hop data indicative of whether ornot the frequency is to be hopped. The error correction data is preparedfrom code data such as a Reed-Solomon code (hereinafter referred to as"RS code"), which is well-known in the art.

According to the present embodiment, the communication device 1 isconstructed as shown in FIG. 14. The communication device 1 of thepresent embodiment is the same as that of the first embodiment exceptthat the control unit 38 is not provided with the dial 39, the memory40, and the timer 41, but is provided with an error rate detectionstorage unit 24 and a comparing unit 23. Although not shown in thedrawing, the control unit 38 is constructed from a CPU, a ROM, and aRAM.

The error rate detection storage unit 24 is for using the well-known RScode error detection technique to calculate an error rate of receiveddata, which has been transmitted from the remote communication deviceand inputted from the demodulator 34. The comparing unit 23 previouslystores therein a predetermined first reference error rate. The comparingunit 23 is for comparing the calculated error rate of the received datawith the predetermined first reference error rate. When the error rateof the received data is higher than the first reference error rate, thecomparing unit 23 determines that satisfactory communication is notpossible at the current frequency. In this case, the comparing unit 23will output a frequency hop instruction signal to the spread code seriesgenerator 26. On the other hand, when the calculated error rate is equalto or lower than the first reference error rate, the comparing unit 23determines that it is possible to achieve satisfactory communication atthe current frequency. The comparing unit 23 therefore will output, tothe spread code series generator 26, a frequency maintain instructionsignal indicating that the frequency should be maintained unchanged. Itis noted that the comparing unit 23 outputs the frequency hopinstruction signal and the frequency maintain instruction signal also tothe primary modulator 37.

According to the present embodiment, therefore, when the communicationdevice 1 is in a transmission slot for transmitting transmission datatoward a remote communication device, the control unit 38 controls thecomparing unit 23 to output the frequency hop instruction signal or thefrequency maintain instruction signal to the primary modulator 37. Theinstruction signals are modulated by the primary modulator 37 and addedas the hop data to the transmission data at the data adding device 36 asshown in FIG. 20. The hop data is transmitted to the remotecommunication device together with transmission data at the currentfrequency. The control unit 38 also outputs the instruction signal tothe spread code series generator 26 so as to update or maintain thefrequency of the frequency-hopping signal at the subsequent receptiontime slot.

During the reception time slot, the control unit 38 receives hop data inreception signals transmitted from the remote communication device 1.When the hop data contains a frequency hop instruction signal, thecontrol unit 35 outputs a frequency hop instruction signal to the spreadcode series generator 26 so that the next frequency will be used duringthe subsequent transmission time slot.

It is now assumed that communication devices 1a and 1b, each of whichhas the structure of FIG. 14, perform bi-directional communicationtherebetween at a certain frequency f1. In this case, when thecommunication device 1a detects, in its reception time slot, that theerror rate of the reception data at the current frequency f1 is higherthan the first reference error rate, the communication device 1a sends,to the communication device 1b, a frequency hop instruction signal ashop data together with transmission data. This data sending operation isperformed at the current frequency f1.

Then, the control unit 38a outputs a hop instruction signal to thespread code series generator 26a, thereby controlling the frequencysynthesizer 28a to generate signals at the next frequency f2.Simultaneously, the communication device 1b receives the hop instructiondata in the reception data. The control unit 38b outputs a hopinstruction signal to the spread code series generator 26b, therebycontrolling the frequency synthesizer 28b to generate signals at thenext frequency f2. Thus, the communication devices 1a and 1bsimultaneously hop to the next frequency f2.

Accordingly, the communication is attained as shown in FIG. 15. Asapparent from the drawing, rather than hopping at regular intervals asin the conceivable communication device, the communication devices ofthe present invention hop to a new frequency only when the error ratecaused by interference becomes too high. As a result, the total amountof occupied time t relative to the total holding time is decreased.

In the same manner as in the first and second embodiments, each of thecommunication devices 1a and 1b repeatedly performs transmissionoperation and reception operation in alternation. That is, thetransmission time slot and the reception time slot are provided inalternation. The reception time slot of the communication device 1b isset to coincide with the transmission time slot of the communicationdevice 1a, and the transmission time slot of the device 1b is set tocoincide with the reception time slot of the device 1a. Accordingly, themultiplex communication is attained. Because one frame is constructedfrom one transmission time slot and one reception time slot, the holdingtime for one frequency can be set to an integral multiple of a frame.The holding time will therefore change each time the frequency ischanged.

As described above, according to the third embodiment, the error rate ofthe received data is detected. The error rate is then compared to thefirst reference value. If the error rate is equal to or smaller than thereference value, no change is made; however, if the error rate is higherthan the first reference value, the communication device changes thespread code to be outputted from the spread code generator 26, therebychanging the frequency used for transmission and reception. This methodenables the device to reduce the number of frequency hops, therebyincreasing the transfer rate.

A first modification of the third embodiment will be described belowwith reference to FIGS. 16 and 18(a), 18(b). and 18(c).

FIG. 16 shows the structure of the wireless communication device 1 ofthe present modification. The device of the modification is the same asthat of the third embodiment of FIG. 14 except that the control unit 38includes a time determining unit 27 provided with a timer 27a.

The timer 27a is for starting timing when the control unit 38 outputs afrequency hop instruction signal to the spread code series generator 26.The timer 27a is designed to be reset to zero and to again start timingwhen another frequency hop instruction signal is outputted.

The time determining unit 27 is for determining whether or not the timecounted by the timer 27a becomes longer than a predetermined referenceholding time. The reference holding time is smaller than the maximumlimit of holding time for the frequency hopping wireless communicationmethod. For example, the reference holding time may be set to severalmilliseconds, while the predetermined maximum limit is 400 milliseconds.The time determining unit 27 is configured to generate a time up signalwhen the timer 27a counts the predetermined reference holding time. Inother words, the time determining unit 27 generates a time up signalwhen the predetermined reference holding time lapses after the frequencyhop instruction signal has been issued at the latest. When the time upsignal is generated, the control unit 38 creates a no good (NG) signal.The NG signal will be sent to the remote communication device as hopdata to instruct frequency hopping.

The comparing unit 23 is configured to generate a communication no good(NG) signal when the error rate of the received signal, as detected bythe error rate detection storage unit 24, becomes higher than the firstreference error rate. The NG signal will be sent to a remotecommunication device as hop data to instruct frequency hopping. Thecomparing unit 23 generates a communication good (OK) signal when theerror rate is equal to or smaller than the first reference error rate.The OK signal will be sent to the remote communication device as hopdata to instruct frequency maintaining.

According to the present modification, when the control unit 38generates a NG signal, the control unit 38 outputs a NG signal(frequency hop instruction signal) to the primary generator 37. The NGsignal is transmitted as hop data to the remote communication devicetogether with transmission data. The control unit 38 also controls thespread code series generator 26 so that communication will be attainedwith the updated frequency during the subsequent reception time slot.

When a NG signal (frequency hopping instruction) is received as hop datafrom the remote communication device during a reception time slot, thecontrol unit 38 controls the spread code series generator 26 beforeperforming the subsequent transmission operation. The timer 27a is resetto zero, and then started when the subsequent transmission operation isstarted with the updated frequency.

According to this modification, the hopping pattern table 35 isconstructed from a memory for storing a plurality of differentfrequencies at respective addresses as shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Frequency series                                                                         Address no.                                                                             1      2    3    4   . . . n                                        Frequencies                                                                             f1     f2   f3   f4  . . . fn                            ______________________________________                                    

The synthesizer 28 is for producing frequency-hopping signals whosefrequency will be changed in the order of f1, f2, . . . , and fn. Whenthe frequency becomes fn, the frequency will be changed again into f1.

The spread code series generator 26 is provided with a memory areaformed with a pair of counters 261 and 262. The counter 262 is for beingset with one address in the hopping table 35. The counter 261 is forbeing set with the address number set in the counter 262. Thesynthesizer 28 is designed to generate a frequency-hopping signal whosefrequency is stored in the table 35 at the address whose number ispresently set in the counter 261.

Similarly to the above-described third embodiment, the data format forthe transmission data (reception data) is as shown in FIG. 20.

Next, bi-directional communication between two communication devices 1aand 1b will be described with reference to flowcharts of FIGS. 18(a),18(b), and 18(c). FIG. 18(c) is a flowchart showing relationship betweenthe timings of the respective processes performed at the communicationdevices 1a and 1b shown in FIGS. 18(a) and 18(b). Each of thecommunication devices 1a and 1b has the same structure as shown in FIG.16. Reference numerals of the respective components in the communicationdevices 1a and 1b are referred to as the same reference numerals in FIG.16 followed with the reference symbols "a" and "b," respectively. It, isnoted that in each communication step, synchronization is attainedbetween the devices 1a and 1b through transmission of synchronizationsignals in the form of the predetermined bit patterns. For simplicityand clarity, the description for the synchronizing processes are omittedfrom the following description.

At the beginning of the process, the communication devices 1a and 1bsimultaneously perform S501 and S601 where the frequency of thefrequency-hopping signal (initial carrier wave frequency) is initiallyset. This operation is performed through initializing the contents ofthe counters 261a, 262a, 261b, and 262b in the devices 1a and 1b. Thatis, all the counters 261a. 262a, 261b, and 262b are initialized into thesame address number "1".

First, the operation of the communication device 1a will be describedwith reference to FIGS. 15(a) and 18(c).

In S502, the counter 261a in the communication device 1a is set to theaddress number presently stored in the counter 262a. Then, in S503,communication is performed between the communication devices 1a and 1bat the frequency corresponding to the address number presently set inthe counters 261a and 261b. In this example, the communication device 1afirst receives data transmitted from the communication device 1b in S504as shown in FIG. 18(c). The hop data, which is a flag, is then separatedfrom the received data. If the hop data is determined in S505 as an NGsignal, it is determined that the communication device 1b has detectedthat the error rate has exceeded the first reference error rate in thelatest-performed reception operation at the current frequency.Accordingly, the program proceeds to S506 where the counter 262a isupdated into data of an address in the table 35 next to the addresspresently set in the counter 262a. Then, transmission data and errorcorrection data, to be sent to the communication device 1b, are createdin S517. At this time, an OK signal is created as hop data. Then, inS518, the counter 261a is set to the address number newly set in thecounter 262a in S506.

On the other hand, if the received hop data is determined in S505 as anOK signal, it is determined that the communication device 1b hasdetected that the error rate has not exceeded the first reference errorrate in the latest-performed reception operation at the currentfrequency. Because it is unnecessary to change the current frequency,the program does not proceed to S506, but proceeds to S507.

In S507, the time determining unit 27 determines whether or not thereference holding time has elapsed from the time when the frequency hasbeen hopped to the current frequency, i.e., the time when thefrequency-hopping signal with the current frequency has started to beoutputted. If the reference time has elapsed ("yes" in S507), it isdetermined that the communication has been performed too long with thecurrent frequency and therefore that the frequency has to be changed.Accordingly, after transmission data and error correction data, to besent to the communication device 1b, are created in S508, the counter262a is updated in S509, and an NG signal is created as hop data inS516.

If the time determining unit 27 determines that the reference holdingtime has not yet elapsed ("no" in S507), on the other hand, it isunnecessary to change the current frequency. In this case, aftertransmission data and error correction data, to be sent to thecommunication device 1b, are created in S510, an error rate of thepresently-received reception data is calculated in S511 based on thereception data and the error correction data received in S504. Also inS511, the calculated error rate is compared with the predetermined firstreference error rate. If the calculated error rate is equal to or lowerthan the first reference ("yes" in S512), it is determined that it isunnecessary to change the current frequency. Accordingly, the programproceeds to S513 where an OK signal is created as hop data. If thecalculated error rate is greater than the first reference error rate("no" in S512), on the other hand, the counter 262a is updated in S509.Then, an NG signal is created as hop data in S516.

Then, in S514, communication is performed between the communicationdevices 1a and 1b at the frequency corresponding to the addresspresently set in the counters 261a and 261b. At this time, thecommunication device 1a sends the created transmission data to thecommunication device 1b in S515. Then, the process returns to S502 wherethe counter 261a is set to the present address number set in the counter262a.

Next, the operation of the communication device 1b will be describedwith reference to FIGS. 18(b) and 18(c). The description will be briefbecause the operation of the communication device 1b is similar to thatof the device 1a.

After the initialization operation at S601, the communication device 1bperforms in S614 communication with the device 1a at the frequencycorresponding to the address number presently set in the counter 261b.At the same time, the device 1a performs the communication operation ofS503. Accordingly, the device 1b transmits transmission data to thedevice 1a in S615. The device 1a receives the data in S504.

Then, in S602, the counter 261b is set to the address number presentlystored in the counter 262b. In S603, then, the device 1b performscommunication again. At the same time, the device 1a performs thecommunication in S514 as shown in FIG. 18(c). The communication isperformed at the frequency presently indicated by the counter 261a inthe communication device 1a and the counter 261b in the communicationdevice 1b. The communication device 1b therefore receives data in S604which is transmitted from the communication device 1a in S515. In thecommunication device 1b, hop data is separated from the received data inS605. If the hop data is determined in S605 to contain an NG signal, thecounter 262b is updated in S606; transmission data and error correctiondata, to be sent to the communication device 1a, are created in 6617,and an OK signal is created as hop data; and the counter 261b is set tothe address number presently set in the counter 262b in S618.

If the hop data is determined in S605 to contain an OK signal, on theother hand, the time determining unit 27b determines whether thereference holding time has elapsed in S607. If the reference holdingtime has elapsed ("yes" in S607), transmission data and error correctiondata, to be sent to the communication device 1a, are created in S608,and the counter 262b is updated in S609. An NG signal is then created ashop data in S616.

If the time determining unit 27 determines that the reference holdingtime has not yet elapsed ("no" in S607), transmission data and errorcorrection data, to be sent to the communication device 1a, are createdin S610. Then, in --S611, an error rate for the current frequency iscalculated based on the transmission data and error correction datareceived in S604. The calculated error rate is compared with the firstreference error rate in S611. If the error rate is equal to or lowerthan the first reference ("yes" in S612), an OK signal is created as hopdata in S613. If the error rate is greater than the reference ("no" inS612), on the other hand, the counter 262b is updated in S609, and an NGsignal is created as hop data in S616.

Then, the program returns to S614 where communication is performedbetween the communication devices 1a and 1b at the frequency indicatedby the addresses presently set in the counters 261a and 261b. At thistime, the communication device 1b sends the created transmission dataand hop data to the communication device 1a in S615. The communicationdevice 1a receives the data in S504.

As described above, according to the present modification, the timer 27amonitors the time that elapses after the frequency has hopped to thecurrent frequency. The device 1 determines whether or not thepredetermined time has passed after the frequency has hopped to thecurrent frequency. The frequency is changed when it is determined thatthe error rate has exceeded the first reference value or when it isdetermined that the predetermined time has elapsed after the latesthopping operation, whichever determination occurs first. Thus, theamount of time communicating at each frequency can be restricted evenwhen error rate is not lowered. Privacy of communication can beprotected.

It is now assumed that the communication device 1a detects thatreception data at frequency f1 has a high error rate in S512. In thiscase, the counter 262a is updated in S509. Then, NG hop data is createdin S516 and is transmitted to the communication device 1b together withtransmission data in S515 (S604). This communication operation isperformed still at the frequency f1. Then, in the device 1a, the counter261a is also updated in S502. In the device 1b, the NG hop data isreceived in S604, and the counter 262b is updated in S606. Then, inS618, the counter 261b is set to the address newly updated in thecounter 262b. Accordingly, at the next communication process of S614(SS03), the device 1b transmits transmission data to the device 1a atthe next frequency f2.

Similarly, it is now assumed that the communication device 1b detectsthat reception data at frequency f2 has a high error rate in 6612. Inthis case, the counter 262b is updated in S609. Then, NG hop data iscreated in S616 and is transmitted to the communication device 1atogether with transmission data in S615 (S504). This communicationoperation is performed still at the frequency f2. Then, in the device1b, the counter 261b is updated in S602. In the device 1a. the NG hopdata is received in S504, and the counter 262a is updated in S506. Then,in S518, the counter 261a is set to the address newly updated in thecounter 262a. Accordingly, at the next communication process of S514(S603), the device 1a transmits transmission data to the device 1b atthe next frequency f3.

FIG. 17 shows a wireless communication device of a second modificationof the third embodiment.

The communication device 1 of the present modification is the same asthat of the above-described first modification of FIG. 16 except thatthe control unit 38 is further provided with a high error ratedetermining unit 39.

In the same manner as in the above-described modification, the controlunit 38 generates an NG signal (frequency hop instruction signal) when atime up signal is generated by the time determining unit 27 or when thecomparing unit 23 determines that the error rate of the reception databecomes higher than the first reference error rate, whichever occursfirst.

The high error rate determining unit 39 is for determining whether ornot the error rate detected by the error rate detection storage unit 24is higher than a second reference error rate, which is higher than thefirst reference error rate. If the error rate is higher than the secondreference error rate, the high error rate determining unit 39 generatesa table changing signal. In response to the table changing signal, thecontrol unit 38 changes the hopping table 35 through removing, from thetable 35, data of the current frequency which has been detected asprovides the high error rate. That is, the control unit 38 removes thefrequency data from the table area to a spare area. The control unit 38may additionally move data of a spare frequency to the addresspreviously occupied by the frequency data just removed. Thus, data ofthe current frequency may be excluded from the hopping table 35, or maybe replaced with another frequency data. Thus, the content of thehopping table 35 can be changed.

Alternatively, the data of the current frequency may be replaced withdata of another frequency whose error rate has already been detected asequal to or lower than the second reference error rate.

Or, when retrieving data of a certain frequency from the hopping table35 for the next communication according to a hop instruction signal, thehigh error rate determining unit 39 may judge whether or not theretrieved frequency has been used previously and has been determined tohave a high error rate, higher than the second reference error rate.When the retrieved frequency has been determined to have a high errorrate, the control unit 38 may control the spread code series generator26 not to use the retrieved frequency, but to use a frequency next tothe retrieved frequency.

Further, it is possible to return the hopping table 35 to its initialstate when the number of changes applied to the hopping table 35 exceedsa reference number or when the number of frequencies set to be usable inthe hopping table 35 fall below a reference number.

According to the present modification, the frequency used when a higherror rate is detected will no longer be used in subsequent cycles fromthe hopping table 35. Thus, by removing frequencies resulting in a higherror rate, the data transfer rate can be increased. The hopping table,and therefore the hopping pattern, is returned to its initial state ifthe total number of available frequencies is determined to fall belowthe reference number. Further, by repeating this process, a privateduplex communication can be attained, and improvements can be made oncommunication privacy with the spread spectrum communication using thefrequency hopping method. Also, it becomes unnecessary for the spreadcode generator to generate PN codes (spread codes) but merely selectcodes or frequencies from the memory (table).

A third modification of the third embodiment will be described belowwith reference to FIG. 19.

According to the present modification, only one of the pair ofcommunication devices 1a and 1b is constructed from the communicationdevice shown in FIG. 16. The other communication device is the same asthe conceivable device shown in FIG. 1. In this example, thecommunication device 1a is structured as shown in FIG. 16, and thecommunication device 1b is structured as shown in FIG. 1. Accordingly,the device 1b is not provided with the error rate detection storage unit24 or the comparing unit 23.

Since the time required to calculate error rates ultimately placesrestrictions on the transfer rate, when the communication device 1b doesnot perform this calculation operation, it is possible to increase thetransfer rate.

In this modification, the communication device 1a performs theoperations exactly the same as those shown in FIG. 18(a). Thecommunication device 1b does not perform the operation oration in FIG.18(b), but performs the operation in FIG. 19. That is, first, in S701,communication is performed at the frequency indicated by the counters261a in the communication device 1a and the counter 261b in thecommunication device 1b. At the same time, the communication device 1aperforms the process of S514. Then, while the communication device 1aperforms the process of S515, the communication device 1b receives datatransmitted from the communication device 1a, and separates the hop datafrom the reception data in S702. Next, in S703, the transmission dataand error correction data are created by the communication device 1b,and sent to the communication device 1a. Then, in S704, the hop datareceived from the device 1a is returned to the device 1a withouteffecting any changes to the hop data. At the same time, the device 1aperforms processes of S502-S504. If the received hop data contains an OKsignal in S705, no further operations are executed. On the other hand,if the hop data contains an NG signal ("NG" in S705), the counter 261bis updated in S706 to hop to the next frequency, which will be usedduring the next reception time slot.

In the above description for the third embodiment and its modifications,the transmission data format shown in FIG. 20 is used. It is obvious,however, that changing the order of the transmission data, errorcorrection data, and hop data would have no adverse effects.

Further, although the control unit 38 is shown mounted in thecommunication device in FIGS. 3, 14, 16, and 17, the control operationof the control unit 38 can be executed by a hardware circuit, softwareprogram, and the like.

As described above, the wireless communication system of the presentinvention is for performing bidirectional communication using afrequency hopping method, during which communication the frequency toswitched. According to the first embodiment, the communication system isdesigned to adjust the length of time for each frequency. Thecommunication system controls communications according to the adjustedholding time. Accordingly, the length of the holding time is change, andcommunication is performed with holding each frequency for the alteredholding time. Because the length of time for communicating at any onefrequency has to be limited in order to maintain privacy and allow theuse of multiple channels, the length of the holding time is ordinarilyset lower than the maximum limit. The closer the holding time gets tothis limit, the fewer times frequency hopping is performed over time andthe smaller the total length of occupied time. Hence, the transmissionrate increases as the holding time nears the limit. On the other hand,if the length of the holding time is shortened, the number of frequencyhopping increases, improving the privacy or secrecy of transmitted data.Thus, the transmission rate can be increased by increasing the holdingtime in order to decrease the occupied time that occurs when frequencyhopping. Conversely, privacy of data can be improved by decreasing theholding time in order to increase the number of frequency hops.

The user can set his/her desired value for the length of the holdingtime to suit the type of data to be sent. For example, if the data beingsent need not be kept private, the holding time can be set long toincrease transfer speed. However, if the data is highly private, theholding time can be set short to improve privacy. Thus, It is possibleto change the holding time to suit the demands of the user, allowingeither the transfer rate or privacy to be improved.

It is desirable that the communication device automatically shortens theholding time when the communication data is voice data and lengthens theholding time when the data is non-voice data. The holding time is thusautomatically shortened during the communication of voice data andlengthened during the communication of non-voice data. This method isused because non-voice data contains a comparatively large volume ofdata, usually making an increase in the transfer rate more importantthan privacy. On the other hand, voice data has a comparatively lowvolume of data, usually making secrecy more important than an increasein the transfer rate.

The communication device may be designed to determine whether eachtransmission contains voice data or non-voice data and to change theholding time to suit the result of that determination. Alternatively,the transmitting device may be designed to send a personal ID signal bywhich the receiving device can determine whether the transmitting devicewill send non-voice data, such as image data from a facsimile device, orvoice data as from a telephone. The receiving device is designed tochange the holding time to correspond to the determined type of data.Thus, it is possible to improve either the transmission rate or privacyby changing the holding time to a value appropriate to the type of databeing transmitted.

In the first embodiment, the communication data contains holding timedata. The holding time is changed in correspondence with the holdingtime data. That is, the transmitting communication device adds holdingtime data to the communication data in every transmission. The length ofthe holding time is determined based on the transmitted holding timedata, setting a longer holding time for non-voice data, such as imagedata, and setting a shorter holding time for voice data. Since theholding time is adjusted based on the holding time data included in thecommunication data, a suitable holding time can be set either toincrease the transmission rate or to increase privacy, depending on thetype of data being transmitted.

Especially when communicating by a packet exchanging method, the holdingtime is changed so that the possible communication time during theactual holding time becomes equal to an integral multiple of the packetlength. According to the packet exchange method, communication data istemporarily stored in the memory buffer, divided into equal blocks or"packets," and transmitted to the other party. Here, if the possiblecommunication time during the actual holding time is not an integralmultiple of the packet length, then there will exist a remainder time,which is the difference between the possible communication time and theintegral multiple of the packet length nearest but not greater than thepossible communication time. No data can be transmitted during thisremainder time. Thus, the transmission rate cannot be sufficientlyincreased. However, if the possible communication time is an integralmultiple of the packet length, then remainder time will not exist andcommunication will be efficient, effectively increasing the transferrate. Therefore, this wireless communication system is effective forincreasing the transfer rate when performing packet exchangecommunication.

Especially when the communication device is stored with the patterns ofchanges to the holding time, the holding time is changed according tothe stored pattern of holding time changes. In this wirelesscommunication system, the holding time for a certain frequency isdetermined by the pattern of holding time changes. The holding time canbe determined each time the frequency changes. Or, the decision whetherto stay with the current frequency or change to another frequency can bemade at set intervals. For example, the decision is repeatedly attainedat the fixed time interval of the basic holding time TH in the secondembodiment, with using the hop data pattern and the hop data flag.However, other various methods can be employed. The above-describedmethods makes it extremely difficult for a third party to interceptcommunication data, because not only does the frequency change, but theholding time also changes. Hence, privacy can be enhanced.

According to the third embodiment, the error rate of the receivedsignals is detected. The communication device previously stores thereinthe error rate reference value. The device determines whether or not thedetected error rate of the received signals is higher than the firstreference value. The frequency of the frequency-hopping signal is hoppedto a next frequency when the error rate is determined higher than thefirst reference value. It is therefore possible to decrease the numberthe frequency hops. Accordingly, the total length of occupied time t canbe decreased. increasing the data transfer rate as a result.

According to the first modification of the third embodiment, time ismonitored after a frequency is hopped to a new frequency. It istherefore possible to restrict the length of time for communication ateach frequency band, since the maximum time limit is predetermined forcommunication at any frequency. It becomes possible to satisfycommunication conditions within this time limit. Because the device isprovided with the hopping pattern table, it is possible to reduce thetotal length of time required to calculate hopping frequencies, therebyincreasing the transfer rate.

According to the second modification of the third embodiment, it ispossible to remove data of frequencies proved to provide a high errorrate. It is possible to prevent the device from using those frequencies.As a result, the number of frequencies to be used is limited, andaccordingly the total amount of occupied time can be decreased,resulting in a corresponding increase in the transfer rate.

While the invention has been described in detail with reference to thespecific embodiments thereof, it would be apparent to those skilled inthe art that various changes and modifications may be made thereinwithout departing from the spirit of the invention.

For example, in the above-described embodiments and modifications, thecommunication device 1 stores therein the hopping pattern table 35.However, the communication device may not store the hopping pattern.When the frequency has to be changed to the next frequency, thecommunication device may calculate a next hopping frequency with using apredetermined calculating formula, a predetermined number train, apredetermined spread code series, or the like.

In this case, according to the third embodiment, when calculating acertain frequency for the next communication according to a hopinstruction signal, the high error rate determining unit 39 may judgewhether or not the calculated frequency has been used previously and hasbeen determined to have a high error rate, higher than the secondreference error rate. When the calculated frequency has been determinedto have a high error rate, the control unit 3B may control the spreadcode series generator 26 not to use the calculated frequency, but tocalculate another frequency.

What is claimed is:
 1. A wireless communication device for performingbi-directional communication with a remote communication device using afrequency hopping method, the device comprising:a frequency changingunit changing a frequency, at which communication is performed; acommunication unit performing communication at the changed frequency fora holding time; a holding time length controlling unit controlling alength of the holding time and controlling the communication unit toperform communications at the changing frequency for the controlledholding time; and a holding time inputting unit allowing a user to inputthe user's desired value as the length of the holding time, the holdingtime length controlling unit changing the length of the holding timeinto the user's inputted value.
 2. A wireless communication device ofclaim 1, further comprising a storing unit storing a frequency changingpattern, according to which the frequency changing unit changes thefrequency.
 3. A wireless communication device as claimed in claim 2,wherein the holding time length controlling unit includes a unit addingholding time data, indicative of the inputted holding time, to thecommunication data in every transmission of communication data.
 4. Awireless communication device of claim 3, wherein the holding timelength controlling unit further includes:a holding time data detectingunit detecting the holding time data contained in the communication datatransmitted from the remote communication device; and a unit changingthe length of the holding time in correspondence with the holding timedata.
 5. A wireless communication device of claim 1, wherein the holdingtime length controlling unit includes:an error rate detecting unitdetecting an error rate of signals received from the remotecommunication device at a present frequency; a memory storing apredetermined error rate reference value; an error rate determining unitdetermining whether or not the detected error rate of the receivedsignals is higher than the predetermined error rate reference value; anda frequency changing control unit controlling the frequency changingunit to change the frequency from the present frequency into anotherfrequency when the error rate determining unit determines that thedetected error rate is higher than the predetermined error ratereference value, the frequency changing control unit controlling thecommunication unit to perform communications according to the changedfrequency.
 6. A wireless communication device of claim 5, wherein theholding time length controlling unit further includes:a timing unitmeasuring time after the frequency is changed; and a time determiningunit determining whether or not the measured time reaches apredetermined time, and wherein the frequency changing control unitcontrols the frequency changing unit to change the frequency at a timingwhich is an earlier one of a timing when the error rate determining unitdetermines that the error rate becomes higher than the error ratereference value and another timing when the time determining unitdetermines that the predetermined time has elapsed.
 7. A wirelesscommunication device of claim 6, further comprising a storing unitstoring a frequency changing pattern, according to which the frequencychanging unit changes the frequency.
 8. A wireless communication deviceof claim 7, further comprising:high a error rate frequency determiningunit for determining mining a frequency whose error rate is determinedby the error rate determining unit to be higher than anotherpredetermined error rate reference value which is higher than thepredetermined error rate reference value; and pattern changing means forchanging the frequency changing pattern stored in the pattern storingmeans through removing the determined frequency from the frequencychanging pattern.
 9. A wireless communication device of claim 8, whereinthe pattern changing unit replaces the determined frequency with anotherfrequency whose error rate has been determined by the high error ratefrequency determining unit to be lower than the other predeterminederror rate reference value.
 10. A wireless communication device forperforming bi-directional communication with a remote communicationdevice using a frequency hopping method, the device comprising:afrequency changing unit changing a frequency, at which communication isperformed; a communication unit performing communication at the changedfrequency for a holding time; a holding time length controlling unitcontrolling a length of the holding time and controlling thecommunication unit to perform communications at the changed frequencyfor the controlled holding time; and a frequency changing patternstoring unit storing a frequency changing pattern, according to whichthe frequency changing unit chances the frequency, wherein the holdingtime length controlling unit sets the holding time to a first value whencommunication data to be communicated by the communication unit is voicedata and sets the holding time to a second value longer than the firstvalue when the data to be communicated by the communication unit isnon-voice data.
 11. A wireless communication device of claim 10, whereinthe holding time length controlling unit includes:a determining unitdetermining whether or not data to be communicated contains voice data;and a holding time changing unit changing the holding time incorrespondence with the determined result.
 12. A wireless communicationdevice of claim 11, wherein the determining unit includes:a detectingunit detecting a type of the communication device; a sending unitsending, to the remote communication device, a personal ID signalindicative of the type of the communication device, thereby allowing theremote communication device, to which the communication is to beperformed, to determine whether or not the subject communication devicewill send voice data.
 13. A wireless communication device for performingbi-directional communication with a remote communication device using afrequency hopping method, the device comprising:a frequency changingunit changing a frequency, at which communication is performed; acommunication unit performing communication at the changed frequency fora holding time; a holding time length controlling unit controlling alength of the holding time and controlling the communication unit toperform communications at the changed frequency for the controlledholding time; and a frequency changing pattern storing unit storing afrequency changing pattern according to which the frequency changingunit changes the frequency, wherein the communication unit communicatespacket data according to a packet exchanging method, the holding timelength controlling unit adjusting the holding time so that a possiblecommunication time during the holding time becomes equal to an integralmultiple of the packet length.
 14. A wireless communication device ofclaim 13, wherein the communication unit includes:a unit temporarilystoring communication data; a unit dividing the communication data intoequal packets; and a unit transmitting the packets to the remotecommunication device.
 15. A wireless communication device of claim 14,wherein the possible communication time during the holding time is equalto a time length obtained by subtracting an occupied time length fromthe length of the holding time.
 16. A wireless communication device forperforming bi-directional communication with a remote communicationdevice using a frequency hopping method, the device comprising:afrequency changing unit changing a frequency, at which communication isperformed; a communication unit performing communication at the changedfrequency for a holding time; a holding time length controlling unitcontrolling a length of the holding time and controlling thecommunication unit to perform communications at the changed frequencyfor the controlled holding time; a frequency changing pattern storingunit storing a frequency changing pattern, according to which thefrequency changing unit changes the frequency; and a holding timechanging pattern storing unit storing a pattern for changing the holdingtime, the holding time length controlling unit changing the holding timeaccording to the pattern stored in the pattern storing unit.
 17. Awireless communication device of claim 16, wherein the holding timelength controlling unit determines the holding time for a certainfrequency the stored pattern each time according to the frequencychanges.
 18. A wireless communication device of claim 16, wherein theholding time length controlling unit determines whether to stay with acurrent frequency or to change to another frequency at set timeintervals.